I agree with you on unsubscribing from the emails, but it works. 86% of the users open, 54% click, 23% replied to the email and only 2% unsubscribed.
At my job with HKSEO/Humankind, this is what I spent my days doing, but I would do 4-5 prototypes at a time, pitch them to the owner, build the 1-2, launch and repeat constantly. Once the product was making a decent amount of money, we would spend more time doing the split testing and on-boarding (which was also split tested).
So I know a single developer can do this on 20% time if they aren't expecting a 1 week turnaround.